FIG. 2.

Repetitive blast exposure increases axon damage in the corpus callosum (CC) and adjacent cingulum. (A,B) Confocal images of coronal sections of the CC from Thy1-YFP-16 mice at 3 days after repetitive sham procedures (rSham; A) or repetitive blast exposure (rBlast; B) showing high magnification of yellow fluorescent protein signal (YFP) within axons and showing 4′,6-diamidino-2-phenylindole (DAPI) nuclear stain in blue. The rSham mice exhibit relatively uniform YFP signal filling of axons viewed longitudinally (A). There are small variations in diameter along the length of the axons. In addition, YFP signal is visible in axons of crossing fibers cut transversely (A; white arrow). An example in an rBlast mouse of an axon with a large, intensely fluorescent YFP-filled enlargement indicative of axon damage (B; red arrow) that is distinct from crossing fiber axons (B; white arrow). (C) Analysis of the frequency distribution indicates an increase in both the number and diameter of YFP accumulations in the CC and cingulum of rBlast mice compared with rSham controls. (D) The rBlast significantly increases the incidence of damaged axons with abnormal YFP localization (thickenings, varicosities, and terminal end bulbs) in the CC and cingulum, compared with rSham mice. (E) YFP accumulations in axonal varicosities are significantly larger in rBlast compared with rSham mice (B). Values are mean ± standard error of the mean (SEM). Two-way analysis of variance (ANOVA) was used with repeated measures, for CC and cingulum within same subjects, and Sidak's post hoc multiple comparisons test. For the procedures, mouse numbers were: rSham group, n = 7 and rBlast group, n = 8. Scale bars = 20 μm (A and B).